Project 4, Dweik) Hyaluronan in Pulmonary Hypertension - Idiopathic pulmonary arterial hypertension (IPAH) is a progressive disease that leads to deterioration in cardiopulmonary function and premature death from right ventricular failure. The pathogenesis of IPAH is not fully understood. Although pulmonary artery smooth muscle cells (PASMCs) are considered a major component of the remodeling process in IPAH, the nature of the primary abnormality that triggers and perpetuates PASMC proliferation in IPAH is unclear. We have recently discovered and reported the novel finding that PASMCs from IPAH lungs spontaneously produce high levels of hyaluronan (HA) and that IPAH patients have higher than normal levels of circulating HA in their blood. We hypothesize that abnormalities in HA amount, modification, and fragmentation result in major regulatory switches directing abnormal smooth muscle cell proliferation, inflammation and vascular remodeling in IPAH. Our specific aims are designed to assess the mechanisms of increased HA production and the regulatory role(s) HA has in perpetuating PASMC proliferation, inflammation, and vascular remodeling in IPAH. Specific Aim 1: Define the mechanism(s) regulating HA production in PASMCs in IPAH. We will evaluate the expression of the different Has and Hyal mRNAs and proteins from PASMCs isolated from lungs of IPAH patients and controls, as well as for smooth muscle cells (SMCs) from other sources, and for other cell types to ascertain the uniqueness of the PASMCs. We will also determine if there are genetic or epigenetic abnormalities regulating HA production in these cells. Specific Aim 2: Determine the role(s) of HA in IPAH. We will accomplish this Aim by studying the functional consequences of the high levels of HA in vascular SMC proliferation and inflammation in IPAH in vivo and ex vivo. We will also correlate HA levels with disease outcomes in patients with IPAH. Specific Aim 3: Uncover the mechanlsm(s) responsible for the proliferative and pro-inflammatory functions of HA in IPAH. We will study this by evaluating the specific HA modification(s) that turn this primarily structural molecule under normal physiological conditions into a molecule that stimulates cell proliferation and inflammation in the IPAH lung.